The proposed work is being undertaken in order to enhance understanding of the regulation of bone formation and resorption, employing as an experimental model isolated bone cells dispered from well differentiated bone. The following areas are being emphasized: first, further definition of the mechanisms of action of major bone- seeking hormones (e.g., parathyroid hormone, calcitonin); second, separation of heterogeneous populations of bone cells into specific structural and functional types; and third, the development of a sensitive biological assay for parathyroid hormone in human serum. Previous studies on the nature of the effects of parathyroid hormone and calcitonin on bone-cell cyclic-AMP and adenyl cyclase metabolism are being extended, and the role of adenosine as an intermediary between parathyroid hormone receptors and plasma membrane-located adenyl cyclase is being determined. Isolated bone cells have been separated on the basis of density, using ficoll gradients; and the characteristics (morphological and biochemical) will be explored. Normal human plasma has been found to increase cyclic AMp in isolated bone cells maintained in primary culture; and in future studies, plasma from hypoparathyroid and hyperparathyroid humans will be tested, as will purified synthetic human parathyroid hormone (amino acids 1-34).